A group of leading public health agencies says current measures to restrict junk food marketing to children have failed and tougher restrictions are needed.

The Obesity Policy Coalition has sent a report to state and federal health ministers, calling on them to forcibly restrict junk food ads targeting children.

The coalition's executive manager, Jane Martin, says there is a clear conflict of interest because the code is regulated by the food industry.

She says the Government's own research backs the coalition's findings that there has been no reduction in advertising exposure to children.

"The reason this is so important is because children's diets are incredibly bad," she said.

"They're eating more and more unhealthy food.

"This food is cheap, heavily promoted, easily available and so we need to look at all the levers we can push, and we know that as part of a comprehensive approach, controls on marketing are absolutely critical."

Ms Martin says something must be done to curb the record levels of childhood obesity.

She says regulating junk food advertising is not the only way to tackle bad eating habits but it is an important factor.

"It's part of a comprehensive approach," she said.

"It has reduced exposure of children to some extent and we know it's a key driver. So it's very important that we address all the drivers of overweight and obesity."

She said parents also need to be conscious of the food their children eat and resist pressure to buy junk food.

"I think parents want the Government to step in now and support them," Ms Martin said.

"Government has been pushing this issue around since the preventative health task force recommended they do something and look to moving beyond self-regulation, if it doesn't work.